Mass flow rate sensor for compressors



Feb- 2 1965 D. B. LE MAY ETAL MASS FLow Rm: sENsoR FOR coMPREssoRs 3Sheets-Sheet 1 Original Filed June l5, 1956 V'ER,

ATTORNEY Feb. 2, 1965 D. B. LE MAY ETAL MASS FLOW RATE SENSOR FORCOMPRESSORS Original Filed June l5, 1956 3 Sheets-Sheet 2 KMZMW Feb. 2,1965 D. B. LE MAY ETAI. 3,167,954

MASS FLOW RATE SENSOR FOR COMPRESSORS Original Filed June 15, 1956 3Sheets-Sheet 3 E 8 83 N 'f5 ,P3 s4 69a -8| oA/v E. L EMAY, w/L ro/v EPARKER, )j cA RLTo/v R RA UL,

ALEXANDER s/LVER, PAUL G. STE/Lv, HoMER .L woon,

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ATTORNEY United States Patent O 3,167,954 MASS FLOW RATE SENSUR EURCQMPRESSRS Dan B. .ile May, Palos 'Verdes Estates, and Witten E1/ertsParker, Encino, talitl, Carlton Hutton Paul, Scottsdale, Ariz.,Alexander Silver, East Woodland Hilis, Calif., Paul G. Stein, Phoenix,Ariz., and Horner tl. Wood, Sherman Oaks, Calif., assignors to TheGarrett Corporation, Los Angeles. Calif., a corporation of Caiifcrnia@riginal application June 15, 1956, Ser. No. 591,591. Divided and thisapplication Apr. 29, 1959, Ser. No.

This invention relates generally to gas turbine engines, and moreparticularly to engines capable of furnishing auxiliary power for use inoperating a variety of airborne aircraft equipment or accessories.

This is a true division of our application Serial No. 591,591, tiledJune 15, 1956, now U.S. Patent No. 3,060,- 686, entitled Augmented GasTurbine Engine and Controls.

The present application is directed to a mass iiow rate sensor shown inassociation with and forming a part of the augmented gas turbine engineand controls of such patent, and reference thereto may be had for a morecomplete understanding of the use oi the instant invention.

An object of this invention is to provide a control mechanism for anauxiliary gas turbine for aircraft which is capable of automaticallycontrolling its own operation under varying conditions of power outputwhen an aircraft is on the ground, or when the aircraft is in flight atvarying altitudes under conditions wherein said auxiliary engine isreceiving augmentation air from the main engine ofthe aircraft.

Another object of the invention is to provide a control mechanism for anauxiliary gas turbine engine having means for operating a variable areanozzle at the inlet of the turbine wheel in response to a ow conditionthrough the compressor, whereby a flow condition through the turbine isautomatically matched with that of the compressor.

Another object of the invention is to provide control mechanism for agas turbine engine having a variable area nozzle at the inlet of theturbine, said nozzle being controlled by a device sensitive to ilowthrough the compressor of the engine, whereby the turbine is matchedwith said compressor when operating at varying speeds, therebymaintaining optimum fuel economy and performance of the engine.

Another object of the invention is to provide control mechanism for agas turbine compressor which is adapted to deliver pneumatic power andwherein a variable area nozzle at the inlet of the turbine is controlledby a device sensing flow through the compressor, whereby flow throughsaid compressor and said turbine may be maintained at optimumconditions, and whereby said variable area nozzle is automaticallyopened to permit additional air to iiow from the compressor through theturbine exhaust to thereby prevent a surge condition of the compressorwhen the demand for pneumatic power therefrom is reduced and a criticalflow condition through said compressor is likely to occur.

Another object of the invention is to provide a gas turbine having novelmeans for sensing iiow through its compressor in accordance with theoperation thereof at varying altitudes.

Another object of the invention is to provide a gas turbine compressorarranged to deliver pneumatic power and having a variable area nozzle atthe inlet of the turbine and a blowor' valve at the outlet of thecompressor, both of which are controlled by a device sensitive to ilowthrough the compressor, whereby a surge condition in the compressor isavoided by the automatic opening of the variable arca nozzle and theblowoff valve when said device senses the approach of a surge conditionin the compresser.

Further objects and advantages of the invention will be apparent fromthe following specification, appended claims and accompanying drawings,in which:

FIG. l is an axial sectional View of a gas turbine compressor to whichcontrol mechanism embodying the present invention has been adapted;

FIG. 2 is a diagrammatic View of the gas turbine compressor shown inFIG. l and having a mass flow sensing mechanism constructed according tothe present invention embodied therein;

FIG. 3 is an enlarged, fragmentary, detailed, diagrammatic View, partlyin section, of the compressor flow sensing device, shown in blockdiagram in FIG. 2 of the drawing.

As shown diagrammatically in FIG. 2 of the drawing, the apparatus ingeneral to which the control mechanism of the present invention isapplied includes a gas turbine l0, a compressor 11 connected with theturbine for operation thereby, and various devices for controlling theoperation oi the turbine and structure associated therewith. The turbinei@ has a wheel 12 connected to a shaft 13 for rotation in response tothe flow of heated gases from a combuster 14 to an exhaust passage 15.Rotary motion of the turbine wheel is transmitted by the shaft 13 to anirnpeller 1d forming a part of the compressor Il, the movement of theimpeller drawing air into the compressor inlet and discharging the airinto a plenum 17 forming a part of the compressor. The plenum 17communicates, as at id, with a second plenum 19 forming part of theturbine, some of the air discharged from the compressor generally beingemployed to support combustion of fuel supplied to the combustor 1d. Avariable area nozzle mechanism, indicated generally at 2t), is providedwith adjustable vanes forming a plurality of Variable area nozzles 2dabetween an inlet manifold 21, communicating with the combustor, and theturbine wheel 12 to control gas iiow to the wheel and consequently therate of operation of the turbine and compressor.

To conduct pneumatic power from the compressor to a peint of use, theplenum i7 has a duct 22 leading therefrom, this duct containing a valve23 to control ilow from the compressor. Mechanism indicated generally bythe numeral 24 is provided to control the operation of the valve 23.

In the operation of compressors lof the type shown herein, there is adanger of a surge condition, which may damage the apparatus, occurringwhen the demand for air delivered by the compressor is suddenly reducedor completely interrupted, such as by the closure of valve 23 in duct22.

To eliminate or prevent the occurrence of surge conditions, two deviceshave been provided, one being an actuating device, designated generallyby the numeral Z5 for the variable area nozzle mechanism 26, and theother being a surge blowoti valve mechanism, generally indicated by thenumeral 26, including a duct section 27 branching from duct 22. Theoperations of the two surge eliminating or preventing Vdevices 25 and 26are under the control of a compressor ilow sensing mechanism forming thesubject matter of the present invention and generally indicated by thenumeral 28. The details of construction and operation of the mechanism2S are set forth hereinafter; the details of construction and operationof devices and controls 24, 25 and 26 are set forth in the patentmentioned above.

As shown in FIG. 1 of the drawing, the compressor 1l, which is commonlyknown as a mixed flow compressor, has a single-stage wheel 16 supportedon the shaft 13 which is rotatably mounted in bearings 33 and 34./Adjacent to the inlet of the compressor 11 are guide varies 35 whichcommunicate with a compressor inlet plenum 36. j The plenum 36 isprovided Ywith an opening 36a, which communicates with atmosphere andserves as an inlet to the plenum 36. Communicating with the outlet ofthe compressor 11 are diffuser vanes 37. These diffuser vanes aredisposed radially and axially, and cornmunicate with a diffuser outletpassage 38, which is substantially annular and extends in a reversedirection with respect Vto flow emerging from the diffuser varies 37.The passage 38 communicates with the compressor output plenum 17, whichsurrounds the diffuser section of the compressor in which the vanes 37are disposed. Communicating with the compressor output plenum 17 is thebleed duct 22 which is arranged Vto conduct compressed air from thecompressor toward a point of use. Associated with the bleed duct 22, asshown in FIG. 2, is the load control valve 23, and the valve controlmechanism, indicated generally at 24, which may be similar to thatdisclosed in the patent application of Alexander Silver for Load ControlValve With inverse Rate Type Compressor Pressure Conserver, Serial No.400,638, filed December 28, 1953, now abandoned in favor of acontinuation-in-part Serial No. 17,221, filed March 23, 1960, now PatentNo. 3,080,- 713, or any other suitable type.

The wheel 12 of the turbine 1) is rotatably mounted in bearings 53 and53a and is connected in driving relation with the shaft 13, and thecompressor impeller 16, by means of a quill shaft 54. The variable areanozzles a are disposed at the inlet of the turbine wheel 12 to controlflow therethrough, in accordance with the various other functions of thegas turbine compressor, as described in the patent mentioned above.

As shown in FIG. 2 of the drawings, a tube 56 communicates with thebleed duct 22 and is connected to a pressure regulator 57 of anysuitable type, having an output pressure conducting tube 58 whichextends to the compressor flow sensing mechanism 28, shown in detail inFIG. 3. An orifice 60 is disposed in the tube 58 upstream of thecompressor flow sensing mechanism to restrict the flow of air thereto.Referring to FIG. 3 of the drawings it will be seen that the flowsensing mechanism is provided with a bleedoff valve element 61. Thisbleedoff valve 61 is operable in response to ow conditions through thecompressor 11 for the purpose of varying control pressure in a signalpressure output tube 62.

A spring 63 tends to move the bleedoff valve 61 toward an open position,which movement is controlled through a stem 64 by a pressure responsivediaphragm 65 positioned in a casing 66. The casing 66 is provided withchambers 67 and 68 communicating with opposite sides of the diaphragm65. A static pressure sensing tube 69 intercommunicates with the chamber67 and the inlet of the compressor 11. One end 70 of the tube 69, whichsenses static pressure at the inlet of compressor 11, is located withina restricted ow area therein. A tube 71 communicating with the chamber63 is provided with an open end 72 directed upstream of the compressorinlet, to sense total pressure therein. Thus, the diaphragm 65, duringoperation of the compressor 11, is subjected to a differential betweentotal and static pressures, which reects Mach number or velocity of flowat the compressor inlet. A spring 73, in the chamber 68, tends to forcethe diaphragm 65 toward the chamber 67 and toward a closing direction ofthe bleedoff valve 61.

Connected to the diaphragm 65 by means of a link 74 is a relativelysmaller diaphragm 75, which is disposed in a casing 76, having chambers77 and 78 communicating with opposite sides of the diaphragm 75. Aspring 79 is connected to the diaphragm 75' and is adjustably supportedin the casing 76 by ascrew 8f). The screw 80 is arranged to adjusttension of the-spring 79 for calibration adjustment to balance that ofthe spring 73. Communicating with the chamber 77 is a tube 81 which isconnected with the compressor plenum 17, whereby compresser outputpressure is sensed on the side of the diaphragm 75 exposed to thechamber 77. A tube 82 extends from chamber 78 and communicates with abranch tube 69a at a point intermediate ow dividing orifices S3 and 84disposed in series therein. The branch tube 69a is connected at one endwith Itube 81 .and at the other with tube 69. The latter end of tube 69amay in some instances be left open to the atmosphere. The flow dividingorifice 83 is a fixed venturi type orifice, the effective area of whichremains constant during all choked conditions of the orifice, eventhough the pressure at the inlet thereof may vary. The flow dividingorifice 83 communicates directly with the tube 81, which sensescompressor output pressure existing in the plenum 17. The orifice 84 isadjustable for calibration purposes and communicates with the compressorinlet pressure, orambient pressure, via tubes 69a and 69.

As shown in PIG. 3 and as used hereinafter, P1 refers to pressureexisting at thev inlet of compressor 11; P2 refers to pressure existingin the compressor outlet plenum 17 and P3 refers to pressure existingbetween the fiow dividing orifices 83 and S4 and in the chamber 78. The

Vorifices 83 and 84, cooperating with the diaphragm 75,

are arranged to reflect pressurevratio across the compressor 10. Duringoperation of the compressor, a pressure differential is created acrossthe diaphragm 75, causing a force thereon which corresponds to thepresssure differential across the compressor 11. It will be understoodthat the pressure differential-across the diaphragm 75 is, therefore,variable in proportion to the pressure differential existing across 'thecompressor 11. This differential across the diaphragm 75 is maintainedby the functioning ofthe orices 83 and 84 in response to the pressuredifferential existing across the compressor 11.

Referring to FIG. 3 of the drawings, it will be seen that P2 exists inchamber 77 and that P3 exists in chamber 78, and since P3 is norm-allylower than P2, a pressure differential exists across the diaphragm whichtends to force the diaphragm'75 Ytoward the chamber 78. The pressuredifferential across the 4diaphragm 75 is changed by a change of P2 inchamber '77; for example, an increase of P2 tends to change thedifferential across the `diaphragm 75, causing it to exert a forcethereon toward the chamber 78. The orifice 83 is a fixed venturi typeorifice, and when operating in choked condition its effective arearemains constant, regardless of changes in pressures at its inlet. Atthe same time, the sharp edged orifice l84, when subjected to a variedpressure at its inlet, experiences a change in its effective area. Thus,with each change in P3 following a change in P2, the effective area ofthe orifice 84 changes slightly, which makes a slight additional changein P3. For example, when P3 increases, the effective area of orifice 84increases slightly, tending to reduce P3 to a slight degree; conversely,when P3 decreases, the opposite effect takes place. Therefore, operationof the orifice 84 has a tendency toward changing the pressuredifferential existing across the diaphragm '75, following changes in P2.It will be understood that the pressure differential across thediaphragm 75 is, therefore, substantially proportional to the absolutevalue of pressure P2, but is varied slightly from linear proportionalitywithY P2 by the correspondence .of the effective area of the-sharp edgedorifice 84 with compressor pressure ratio PSL/P1. This effect providesfor a non-linear function corresponding to a desired compressorperformance curve which represents the most efiicient functionalrelationship of a particular compressor with respect to compressorpressure ratio and mass flow. Normally, forces acting von the diaphragmbalance those acting on the diaphragm 75, whereby a modulating action ofthe bleedoff valve 61 provides signal control pressure inthe tube 62 forcontrolling operation of an actuator 25, described in detail in PatentNo. 3,060,686, which controls the variable area nozzle mechanism 2) ofthe turbine. The nozzles 20u, when moved further in an opening directionbythe mechanism 20, allow an increase in ow from the compressor 1l;thus, the nozzles 2da have a direct effect upon Mach number or velocityof iiow at the entrance to the compressor l1. Since weight ilow througha compressor is directly related to the pressure ratio thereacross, whenconsidering the eifrciency of the compressor or its approach to a surgecondition, the variable area nozzles a must automatically be adjustedaccording to these factors. The diaphragm 75, `sensing a function ofcompressor outlet pressure, cooperates with the diaphragm 65, whichsenses compressor inlet Mach number, to provide desired flow through thecompresser. For example, when a reduced flow condition through thecompressor occurs, this condition is sensed by the tubes 69 and 71communicating with chambers 67 and 63 at opposite sides of the diaphragm65, whereupon the differential force across the diaphragm 6:3' isreduced. At the same time, assuming constant speed operation, a slightincrease in PZ/Pl occurs. The combination of these pressures causesdiaphragms 65 and 75 to move in a direction to permit bleedolf valve 61to open Wider and cause venting of the signal control pres sure tube 62.This action causes a reduced pressure sig nal which is transmitted tothe actuator 25, causing it to further open the variable area nozzles20a and to permit an increased dow through the compressor 1l, thusavoiding a surge condition thereof. This increased low condition throughthe compressor then is sensed by the tubes 69 and 71 communicating withchambers 67 and 63 at opposite sides of the diaphragm 65, whereupon thedifferential force across the diaphragm 65 again balances that acrossthe diaphragm 75. It will be understood that total pressure sensed bythe tube 71 is greater, relative to static pressure in the tube 69, withan increase in Mach number of .dow through the compressor 11. Modulationof the valve element 6l thus establishes a control pressure output inthe tube d2, which schedules a desired Mach number of flow entering thecompressor, relative to P2/ Pl.

Assuming that the variable area nozzles 20a are in an over-capacity,open position, causing a mismatch of flow through the turbine lill,relative to flow through the compressor lll, the following operation mayoccur:

When the Mach number of flow entering the compressor is thus increased,relative to a reduced pressure ratio across the compressor. a resultingunbalance of the diaphragms 65 and 75 causes them to move the valve 61toward a closed position, resulting in an increase of control pressurein the control pressure output tube 62. This increased control pressurecauses actuator to move the variable area nozzles toward a closedposition, which thereby matches flow through the turbine tu, relative toflow through the compressor in a manner to restore the desired pressureratio across the compressor Ill, relative to Mach number of flowentering the compressor, and thereby effect an efficient operatingcondition thereof.

From the foregoing, will be understood that the general function of theow sensing device 28, relative to the compressor il, is to schedule theMach number of flow at the compressor inlet according to compressorpressure ratio. llnlet Mach number is a function of compressor inletdifferential pressure (iiow differential) divided by inlet totalpressure. Pressure ratio is compressor outlet pressure divided bycompressor inlet total pressure. Therefore, the ratio of diaphragms 65and 75 and the area ratio of the flow dividers 83 and 8d may be variedaccording to a desired control function of the device 23 to matchoperating characteristics of various gas turbines. A further minoramount of nonlinear adjustment of the controller characteristics may beaccomplished by varying the degree to which the vena contracta of theorifice 34 is suppressed by orifice shape, a sharp edged orifice beingone extreme and a venturi shaped nozzle being the opposite extreme.

According to the present invention, the turbine 12 is provided with aplurality of variable area nozzles 20a which are opened in response to areduced ow condition in the compressor when it approaches a surgecondition. As hereinbefore described, the tiow sensing device 28gencrates a reduced pressure signal in the tube 62 when a reduced howcondition exists in the compressor 1l. The signal control pressure tube62 communicates with the variable area nozzle actuator 25, the detailsof which are disclosed in Patent No. 3,060,686, and transmits signalcontrol pressure impulses thereto.

Communicating with the compressor bleed duct 22 is the branch duct 27 ofthe surge blowoif valve mechanism 26. The surge blowoff valve mechanism26 is arranged to receive a signal from the flow sensing device 28 whena reduced flow condition exists in compressor 1l, whereby a valveelement T126 in the duct 27 is opened -to avert an impending surgecondition in the compressor, in the event such a condition is not firstrelieved by opening of the variable area nozzles 20a by the actuatingdevice 25 cooperating with the flow sensor 28 as hereinabeforedescribed.

Details of the surge blowoif van/e 255 and operations thereof are forthin Patent No. 3,060,686.

A reduced pressure signal generated by the iiow sensing device 2S causesthe valve 126 to open and prevent a surge condition in the compressoril@ by permitting an increased flow therethrough. lt will be noted thatthe variable area nozzle actuator 25 is responsive to a signal magnitudewhich is nominal compared to that which causes operation of the surgerelief valve 126. Thus, the surge relief valve 126 responds with aslight delay as compared to response of the variable area nozzleactuator 25. In this manner, the surge relief valve i296 opens after thevariable area nozzles 20a have rst opened to avert a surge condition inthe compressor Ill. In the event signal magnitude is nominal, the surgerelief valve 126 may not open following surge relief operation of thevariable area nozzle actuator 25. In addition, it will be understoodthat the variable area nozzle actuator 25, having high pressurehydraulic fluid delivered thereto, is capable of opening the variablearea nozzles 20a more rapidly than opening operation of the valve 126 byattendant pneumatic forces which are of considerably lower p.s.i.

When the gas turbine compressor is not operating, reduced pressurepermits the butterfly valve X26 to remain in open position. Duringstarting operations of the gas turbine compressor, the valve 126 must beclosed in order to permit the compressor 11 to build up suicientpressure to support combustion in the combustor 14 and to accelerate theturbine it). The valve 126 is held closed by hydraulic pressure from thegas turbine lubrication pump until compressor output pressure reaches apredetermined value, whereby output dow from the compressor will not bebled off until said compressor output pressure is of sufficientmagnitude to cause the turbine to reach approximately 7S percent of itsoperating speed, as described in Patent No. 3,060,686.

While the mass flow rate sensor forming the subject matter of theinvention has been illustrated as furnishing control signals to surgeblowotf valve control mechanism and variable area nozzle actuators, itmay also oe used to provide control signals for any other suitableapparatus which it is desired to control in accordance with mass iiowthrough a compressor.

We claim:

1. A mass flow sensor for compressors, comprising: total and staticpressure sensing conduits formed for communication with the inlet of acompressor; first movable means having opposed surfaces communicatingwith said pressure sensing conduits and responsive to a differentialbetween fluid pressures therein; a second pressure responsive movablemeans having opposed surfaces, said second pressure responsive meansbein" connected to said first movable means; a first passage meansformed for communication with the outlet of the compressor and one'surface of said second pressure responsive movable means; asecondpassage having first and second pressure dividing orilices in seriestherein, said second passage communicating with said first passage meansand a region of reduced pressure; means communicating with said secondpassage at a point between said orifices and the opposite side of saidsecond pressure responsive movable means; a control pressure conduitcommunicating with said mass flow sensor for supplying fluid underpressure thereto; and a valve communicating with said control pressureconduit and operable by said first and second movable means to provide apneumatic signal by modifying pressure of said fluid in said controlpressure' conduit in accordance with changes of mass flow through the`compressor.

2. A mass HOW sensor for compressors comprising: ltotal and staticpressure sensing conduits communicating with the inlet of a compressor;a first movable means yhaving opposed surfaces communicating with saidpressure sensing conduits and responsive to a differential between fluidpressures therein; a second movable means having opposed surfaces ofdierent areas than those of said first movable means, said secondmovable means be- -ing connected to said rst movable means; a passagemeans disposed to establish communication between the outlet of thecompressor and one surface of said second movable means; a branchpassage having first and second pressure dividing orifices in serieswith each other, said branch passage communicating with said passagemeans and a region of lower pressure; conduit means communicating withsaid branch passage between said orifices and the opposite surface ofsaid second movable means; means forming a valve chamber for receivingkcontrol fluid pressure from a source thereof; and a valve in said valvechamber, said valve being operatively connected with said first andsecond movable means to provide a signal by modifying pressure of saidfluid in said valve chamber in accordance with changes of mass flowthrough the compressor.

3. A mass flow sensor for compressors of the type having an inlet and anoutlet comprising: rst and second fluid pressure responsive elementsconnected for movement in unison; means for directing fluid pressuresconforming to the total and static pressures at the inlet of acompressor to opposed portions of said rst uid pressure responsiveelement; means for directing fluid pressure conforming to compressoroutlet pressure to one portion of said second luid pressure responsiveelement to oppose the forcey of the Huid pressure conforming to thetotal pressure; means including a pair of sonic nozzles in seriesthrough which uid pressure conforming to compressor outlet pressure ispassed to a region of lower pressure to create a reference pressure andapply the same to an opposed portion of said second fluid pressureresponsive element; and means actuated by said fluid pressure responsiveelements to cause a variable signal.

4. A mass ilow sensor for compressors of the type having an inlet and anoutlety comprising: rst and second fluid pressure responsive elementsconnected for movement in unison; resilient means tending to move saidelements in one direction; means for directing fluid pressuresconforming to the total and static pressures at the inlet of acompressor to opposed portions of said first fluid pressure responsiveelement; means for directing a iuidpressure conforming to compressoroutlet pressure to one portion of said second fluid pressure responsiveelement to oppose the force of the uid pressure conforming to said totalpressure; passage means having a pair of serially arranged sonic nozzlesthrough which fluid under pressure conforming to that in the compressoroutlet is passed to a region of lower pressure, fluid flow through saidnozzles producing a reference pressure in 'determined relation to thefluid pressure conforming to compressor outlet pressure; and means forapplying iluid Vment in unison; resilient means tending to move saidelements in one direction; adjustable means for varying the force ofsaid resilient means; means for directing uid pressures conforming tothe total and static pressures at the inlet of `a compressor to opposedportions of said nst fluid pressure responsive element; means fordirecting fluid pressure conforming to the compressor outlet pressure toone portion of said second lluid pressure responsive element to opposethe force of the fluid pressure conforming to the total pressure;passage means having a pair of serially arranged sonic nozzles throughwhich fluid under pressure conforming to that in the compressor outletis passed to a region of lower pressure, fluid flow through said nozzlesproducing a reference pressure in the passage means between said nozzlesbearing a predetermined relation to the iluid pressure conforming tocompressor outlet pressure; and means for applying fluid from saidpassage means at a point between said sonic nozzles to an opposedportion of said second iluid pressure responsive element, said fluidpressure responsive elements being moved in response to pressurevariations applied thereto to actuate a signal transmitting means.

6. A mass flow sensor for compressors of the type having an inlet and anoutlet comprising: first and second lluid pressure responsive elementsconnected for movement in unison; means for directing duid pressuresconforming to the total and static pressures at the inlet of Vacompressor to opposed portions of said lirst fluid pressure responsiveelement; means for directing fluid pressure conforming to compressoroutlet pressure to one portion of said second fluid pressure responsiveelement to oppose the force of the uid pressure conforming to the totalpressure; passage means having a pair of sonic nozzles through whichfluid pressure conforming to that in the compressor outlet is passed toa region of lower pressure, fluid llow through said nozzles producing areference pressure in the passage means between said nozzles bearing apredetermined relation to the pressure conforming to the compressoroutlet pressure; means for varying the effective area of one of saidsonic nozzles; and means for applying fluid from said passage means at apoint between said sonic nozzles to an opposed portion of said secondfluid pressure responsive element, said duid pressure responsiveelements being moved in response to pressure variations applied theretoto actuate a signal transmitting means.

7. A mass ow sensor for compressors of the type having an inlet and anoutlet comprising: a pair of fluid ,pressure responsive elementsconnected for movement in unison, said elements having a predetermineddifferential in areas; means for directing fluid under pressureconforming to the total pressure at the inlet of a compressor to theelement with the greater area to tend to move said elements in onedirection; means for directing duid under pressure conforming to that inthe compressor outlet to the element with the smaller area to tend tomove said elements in the opposite direction; and means for applying areference pressure to the element with the smaller area to opposemovement by the fluid pressure conforming to the compressor outletpressure, said last named means having a series of sonic nozzles throughwhich fluid under a pressure conforming to that in the compressor outletflows to a region of lower pressure, the referencepressurebeing takenfrom between two nozzles in said series, said pressure responsiveelements being moved in response to pressure variations applied theretoto actuate a signal transmitting means.

8. A mass flow sensor comprising: total and static pressure sensingconduits; a first movable means having opposed surfaces communicatingwith said pressure sensing conduits and responsive to a differentialbetween fluid pressures therein; a second pressure responsive movablemeans having opposed surfaces, said second pressure responsive meansbeing connected to said first movable means; a first passage meansformed for communication with a source of variable pressure and onesurface of said second pressure responsive movable means; a secondpassage having first and second pressure dividing orifices in seriestherein, said second passage communicating with said first passage meansand a region of reduced pressure; means communicating with ysaid secondpassage at a point between said orifices and the opposite side of saidsecond pressure responsive movable means; a control pressure conduitcommunicating with said mass flow sensor for supplying fluid underpressure thereto; and a valve communicating with said control pressureconduit and operable by said first and second movable means to provide apneumatic signal by modifying pressure of said fluid in said controlpressure conduit in accordance with changes in pressures in said totaland static pressure sensing conduits and said first passage means.

9. A mass flow sensor comprising: total and static pressure sensingconduits; a first movable means having opposed surfaces communicatingwith said pressure sensing conduits and responsive to a differentialbetween fluid pressures therein; a second movable means having opposedsurfaces of different areas than those of said first movable means, saidsecond movable means being connected to said first movable means; afirst passage means disposed to establish communication between a sourceof variable pressure and one surface of said second movable means; abranch passage having first and second pressure dividing orifices inseries therein, said branch passage communicating with said firstpassage means and a region of lower pressure; conduit meanscommunicating with said branch passage between said orifices and theopposite side of said second movable means; means forming a valvechamber for :receiving control fluid pressure from a source thereof; anda valve in said valve chamber, said valve being operatively connectedwith said first and second moable means to provide a fluid pressuresignal by modifying the pressure in said valve chamber in accordancewith changes in pressure in said total and static pressure sensingconduits and in said first passage means.

10. A mass flow sensor comprising: first and second fluid pressureresponsive elements connected for movement in unison; means for applyingtotal and static pressures to opposed portions of said first fluidpressure responsive element; means for applying fluid pressure from asource thereof to one portion of said second fluid pressure responsiveelement to oppose the force of said total pressure; and means includinga pair of sonic nozzles in series through which fluid pressure from thepreviously mentioned source is passed to a region of lower pressure tocreate a reference pressure and apply the same to an opposed portion ofsaid second fluid pressure responsive element, said pressure responsiveelements being moved in response to variations in pressure appliedthereto to actuate a signal transmitting means.

11. A mass flow sensor comprising: first and second fluid pressureresponsive elements connected for movement in unison; means for applyingtotal and static pressures to opposed portions of said first fluidpressure responsive element; means for applying fluid pressure from asource thereof to one portion of said second fluid pressure responsiveelement to oppose the force of said total pressure; means including apair of sonic nozzles in series through which fluid pressure from t-hepreviously mentioned source is passed to a region of lower pressure tocreate a reference pressure and apply the Same to an opposed portion ofsaid second fluid pressure responsive element; and means actuated bysaid fluid pressure responsive elements to cause a variable signal.

References Cited in the ille of this patent UNITED STATES PATENTS1,129,073 Connet Feb. 23, 1915 2,487,679 Stover Nov. 8, 1949 2,507,075Wiegand et al. May 9, 1950 2,628,086 Cutler Feb. 10, 1953 2,863,601Torell Dec. 9, 1958 2,886,968 Johnson et al. May 19, 1959 FOREIGNPATENTS 486,531 France `an. 21, 1918 20,706 France Nov. 30, 1918 190,121Great Britain Mar. 31, 1924

3. A MASS FLOW SENSOR FOR COMPRESSORS OF THE TYPE HAVING AN INLET AND ANOUTLET COMPRISING: FIRST AND SECOND FLUID PRESSURE RESPONSIVE ELEMENTSCONNECTED FOR MOVEMENT IN UNISON; MEANS FOR DIRECTING FLUID PRESSURESCONFORMING TO THE TOTAL AND STATIC PRESSURES AT THE INLET OF ACOMPRESSOR TO OPPOSED PORTIONS OF SAID FIRST FLUID PRESSURE RESPONSIVEELEMENT; MEANS FOR DIRECTING FLUID PRESSURE CONFORMING TO COMPRESSOROUTLET PRESSURE TO ONE PORTION OF SAID SECOND FLUID PRESSURE RESPONSIVEELEMENT TO OPPOSE THE FORCE OF THE FLUID PRESSURE CONFORMING TO THETOTAL PRESSURE; MEANS INCLUDING A PAIR OF SONIC NOZZLES IN SERIESTHROUGH WHICH FLUID PRESSURE CONFORMING TO COMPRESSOR OUTLET PRESSURE ISPASSED TO A REGION OF LOWER PRESSURE TO CREATE A REFERENCE PRESSURE ANDAPPLY THE SAME TO AN OPPOSED PORTION OF SAID SECOND FLUID PRESSURERESPONSIVE ELEMENT; AND MEANS ACTUATED BY SAID FLUID PRESSURE RESPONSIVEELEMENTS TO CAUSE A VARIABLE SIGNAL.